The ability to automatically count people passing through a given area using video surveillance has many applications. In a typical application, a video camera is placed above an area and people passing through a field of view (FOV) are counted using a technique that is capable of identifying people. For instance, a moving object that meets some size range can be identified as a person.
Accordingly, the selection of the size range in a camera FOV is a critical process in any people counting system that is based on object detection and tracking techniques. This selection directly affects the accuracy of the counting results and is particularly important when multiple people are walking closely to each other in a group. In a group case, the counting system must know accurate person size information to deduce the number of people in the group.
Due to various reasons, single persons often appear with different sizes in the same camera FOV. One of these reasons is the different anthropometric characteristics of human bodies. These characteristics include, e.g., human height, stretch, weight, bust, etc., and determine the shape of each person. In addition, these characteristics cause different sizes of human shadows to be generated when a light source is present in the scene. Another significant cause of different human sizes in camera FOV is the perspective projection effects of the camera. If the camera is at the infinite distance from the monitoring scene, the perspective effects can be ignored. However, this is the ideal case and not realistic in any of the real life situations. As demonstrated in FIG. 2, due to the perspective effects of a normal overhead camera 220, persons with the same size in the real scene 230 will have significant difference between their projected blob sizes in the image 210.
A common shortcoming of many current in-market vision-based people counting systems is the use of global person size parameters, either pre-defined or learned from the training samples. They are not able to effectively handle the size variation situations described above. In such systems, overhead cameras are deployed that require very restricted intrinsic and extrinsic settings about the camera and the settings of the monitoring scenes, such that the walking persons are limited to pass through areas that do not have significant camera perspective effects and/or only allow small size groups of people (a single person or two) passing through. However, in many situations, organizations already have their own cameras installed and would like to utilize these cameras to perform counting tasks. Unfortunately, the aforementioned systems are very difficult to be generalized to handle the counting task in these situations, and many times fail to provide accurate counting results due to their inability to determine the appropriate person size information. Accordingly, a need exists for a person counting system that can address these as well as other issues.